I dont have a merlin, but have you changed the prefilter/s? I know with my ro that the carbon prefilters take out the chlorine, but mine only last 6 months no matter how much or little water's gone through them, after 6 months they dont remove the chlorine and then the chlorine attacks the membranes.
Someone else will be along soon who has a merlin and will give a better explaination.
Tim